Although image guided surgery (IGS) is revolutionizing ENT- and neurosurgery, its utility is limited by two factors. First, the mandatory step of co-registering the preoperative scan (either CT or MRI) with the coordinate system of the patient and operating room is cumbersome, time consuming, and introduces inaccuracies. Second, tissue changes during surgery render the preoperative scans less and less accurate as the surgery progresses. An interactive intraoperative imaging tool that is fully integrated with the imageguided surgery system to provide periodic update scans would solve both problems and would thus increase the accuracy and ease of performing surgery. However, solutions proposed so far - intraoperative ultrasound, MRI, mobile (but in essence conventional) CT, and C-arms with 3D capabilities - have failed because they either are difficult to use, are expensive, produce poor images, or are incompatible with existing operating rooms. We propose to develop a compact intraoperative cone-beam CT imaging tool that will be highly interactive and will allow the surgeon to perform periodic update scans. The long-term aims of the proposed work are to 1) develop a relatively low-cost and compact hardware platform appropriate for an OR setting 2) develop novel techniques to provide multiple intraoperative image acquisitions at reduced radiation dose using reduced field of view acquisitions and 3) conduct initial performance testing demonstrating the improved accuracy over traditional IGS systems. For this Phase I effort we propose to focus on the specific aim of using reduced field-of-view, intraoperative scans to update a region of interest. Such a protocol will greatly reduce radiation dose and will allow for multiple intraoperative scans. Intraoperative scans themselves will facilitate accurate registration of the patient and the IGS system, whereas additional scans can be used to monitor the progression of a surgical procedure and to provide postoperative surgical assessment.